Ignition apparatus



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Aug. 21, 1956 F. T. ANDERSON IGNITION APPARATUS Filed May 2l, 1953 11 l16 niililili' dmxxgg C l e q- 5% B1 I N V EN TOR. FRA MK2. 11V 7.'ANDERSON AGE/VT United States Patent() IGNITION APPARATUS ApplicationMay 21, 1953, Serial No. 356,548

4 Claims. (Cl. 174-35) This invention relates to improvements inignition apparatus. In particular, the invention is directed toimprovements in sealed, high tension spark plug connections for aircraftpower plants.

The spark plug for an aircraft engine, either reciprocating or turbine,must withstand conditions of relatively high temperature of the order ofve hundred degrees Fahrenheit. To conduct current to the plug, a leadconsisting of high tension cable is required, the lead being necessarilyshielded to prevent the emanation of radio frequency current. A suitableconnection is required to join the cable with the spark plug and theshield with the plug body. Like the plug, the components of theconnection must be adapted for high temperature and, for optimumoperation characteristics, the connection should afford the greatestpossible protection against misfiring due to ilasho-ver from the currentcarrying conductor to ground, the likelihood of which increases ashigher altitudes are attained where the danger of ionization of the airor gas is present in the vicinity of the high tension connection.

It is accordingly an object of this invention to provide a novelshielded spark plug connection which will withstand these highertemperature services with. a minimum possibility of flashover at highaltitude.

A further object of the invention is to provide a connection for a sparkplug wherein the zone of the disconnectib'le electrode connection withinthe plug is sealed from the surrounding areas, and one which may bereadily made-up and disconnected.

A still further object is to provide a rugged but simple, long lifeconnection for shielded spark plugs which will satisfy the mechanicalrequirements of spark plug service and which may readily be fabricatedof known ymaterials and according to known practices.

With these and other .objectives in mind which will become apparentduring a consideration of a preferred physical embodiment of theinvention disclosed herein, the present invention contemplates the usualtype of shielded high tension spark plug and flexible shielding conduitthrough which a high tension cable is directed from a source of current.The customary .spherical seat ferrule is attached to the conduit to makeup with the internal chamfer of the shielding barrel of the plug andassociated therewith is a generally accepted internal electricalcontact. For an understanding of the novel features of the invention andtheir association with the abovementioned known parts, reference is madeto the accompanying drawing forming a part of this specification, inwhich* Figure l is a longitudinal cross-section view showing theimproved connection of the invention,

Figure 2 is a view similar to Figure l with the electrical andmechanical joints fully secured,

Figure 3 is a perspective view showing components of the inner seal ofthe invention, and

Figure 4 is a fragmentary View in cross-section of modified elements inthe made-up position of Figure 2.

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Referring to Figures l and 2, numeral 10 indicates the well knownshielded aircraft spark plug, only the connection portion of which isshown, centrally of which is the metallic electrode 11 which isinsulated from the metallic plug shell by a fixe-d ceramic insulatingbushing 12, the right hand end of which is hollow, terminating in ashoulder portion within the plug for a grommet seal. Electricalconnection is effected within plug 10 by means of a helical compressionspring 13 carrying current transmitted to the plug by the high tensioncable 14, the latter extending from a suitable source, not shown,through a shielding flexible conduit 15. Conduit 15 is preferably ofconvoluted or bellows construction armored with the usual braid wire, onthe terminal end of which is attached a ferrule 16 which closes againstthe spark plug barrel. Swivelably engaged over ferrule 16 is the sparkplug nut 17 adapted to draw the ferrule against the plug into rmshielding Contact.

Connection spring 13, providing the direct high tension connection with-spark plug electrode 11 is nested in a known style of cylindricalretainer 2t), electrical continuity between the :spring and retainerbeing had by brazing or otherwise joining the parts. A through `holedrilled axially of the retainer 20 permits the stranded conductor 18 ofcable 14 to be threaded therethrough and secured as by the use of asmall brass nail 19. A spot of solder or brazing material is used tocover the head of the nail further securing the stranded conductor 18 toretainer 2u, and serving also to seal the hole.

A combination grommet and sleeve member 21, preferably of Teflon, istted over the end of cable 14 and encloses the necked down end ofretainer 20 to abutment with the enlarged portion thereof which formsthe well for spring 13. By adhering to an interference t between sleeve21 and retainer 26, an hermetic seal is effected therebetween. Furthersealing the space surrounding the connection between spring 13 andelectrode 11, as will be hereinafter more fully understood, is theengagement of the central flange portion of sleeve 21 and the open endof ceramic bushing insulator 12.

To eifect pressure contact between the ange of sleeve 21 and insulator121, 1 employ a pre-loaded spring assembly comprising a helicalcompression spring 22 and a, hollow spring carrier 23, see Figure 3, thefree length L1 `of spring 22, as shown in the upper section of the View,being foreshortened to L2 by confinement between the end :shoulders 26and 27 on the carrier as illustrated in the phantom position below.Referring again to Figure 1, the spring carrier 23 with spring 22 isdisposed over the right hand Acylindrical end `of the Teflon sleeve 21with the internally chamfered end at the location of shoulder 26 matingwith a corresponding tapered surface on the ange of insulator 21. On theopposite end of carrier 23 the spring overextends shoulder 27diametrically to seat within the major bore B of ferrule 16. To theright of bore B is a somewhat smaller bore B--1 which will accommodatethe right hand shoulder end of carrier 23 and a further bore B-2adjacent bore B-l in the ferrule 16 will admit the cylindrical end ofsleeve 21. To the right 4of bore B-Z is a clearance bore C for the cable14 to extend into flexible tube 15.

In the position of Figure l Athe connection has been made-up just to thepositive abutment of the flange of sleeve 21 against the ceramic bushing12. At this point there has been the slight compression of connectorspring 13 against electrode 11 to ensure electrical continuity. SpaceS-1 remains between the internal chamfer 24 on the shielding body of thespark plug and the spherical seat 25 at the end of ferrule 16. Nut 17has been threaded over the plug body for the first few turns but spring22 has not been acted upon by the closure of the joint at this position.Thereafter, as nut 17 is threaded 3 to full engagement, as shown inFigure 2, space S-l disappears to the extent that the faces 24 and 25are in pressure contact. At the same time, the coil spring 22 has beensubstantially fully compressed thus urging carrier ..3 against sleeve 21which, in turn, will be pressed into sealing engagement with the end ofinsulator 12, completely closing the electrode contact zone.

During closure of the joint, shoulder 27 will move into bore B-l and theend of sleeve 21 will extend further into bore B-Z. It will be noted atthis point, that ferrule 16 moves somewhat with respect to cable i4, thelatter of which must remain in a fixed position during closure. Byregulating the pre-loaded length L-Z and the corresponding elements ofthe connection, this relative movement of the shielding and cable may bekept advantageously small so that practically no buckling of the cablewill result. At the same time, the full effectiveness of spring 22 maybe had to produce a tight contact Zone seal and furthermore, this sealmay be had within the limits of a few threads of the shieldingconnection. The latter result is an advantage when it is considered thatthe initial make-up is effected without resistance except for thatoffered by the relatively minor effect of spring 13 used for electrodecontact. By preloading a spring having optimum dellection versuspressure characteristics over the range of tolerances experienced withsuch connections, l thus attain the make-up advantage indicated withoutresorting to less desirable spring characteristics tending either togive poor seal or to overstress sleeve 21.

While the sleeve 21 may be constructed suiciently long and with asufficiently tight fit over cable 14 to prevent internal ashover fromretainer along the cable surface and to ground under normalcircumstances, in cases where extreme altitude is experienced there isthe increased possibility of such flashover. To avoid this type offailure I provide the components as modified according to Figure 4 withsleeve 21 sharply tapered as at 28 and extended through clearance C witha reduced section 29. In place of bore B-2 in ferrule 16, Figures l and2, I substitute a tapered bore B-3 of deliberate mismatch with thetapered portion 28 of sleeve 2.1 and in interference therewith duringmake-up of the connection. Closure of the joint tends to constrict thesleeve 21 into firm, sealed engagement with the insulation of cable 14and to thus prevent ionization of air between the cable and sleevehowever slight, which would otherwise tend to shorten the effective pathfrom high tension to ground. The mis-match of taper 23 and bore B-3further makes this a possibility without losing the advantage ofinitially unrestricted make-up.

While I have herein illustrated my improvements in combination with thecoil spring type of high tension connection, it is to be understood thatthis is illustrative only, and that the invention may be used with pintypes of electrical connection which also require a pressure seal. It isalso to be understood that the details in the foregoing are illustrativeof a preferred physical embodiment of the invention and that changes maybe made in the size, shape and material of the components of theinvention without departing from the scope of the subjoined claim orclaims.

Having thus described my invention, I claim:

l. In apparatus of the class described, in combination, a spark plugincluding a central electrode and a shielding shell and havinginsulation therebetween, a shielded current conducting cable terminatingin a connector projectlng from its shield and adapted to contact thespark plug electrode within the confines of the shell insulator, a

grommet and insulating sleeve covering said conducting: cable within thespark plug shell, Said gronimet and sleeve flanged to seal against theshell insulator and extending into the cable shield, means to connectthe cable` shield and spark plug Shell a hollow, tubular spring carrierdisposed over said grommet and sleeve extending between the ange thereonand the cable shield and telescopic within the shield, and a compressionspring pre-loaded on said carrier and further compressible between saidcarrier and the cable shield.

2. .ln a connection for a high tension spark plug of the type having ashielding shell insulated from the central electrode, in combination, aninsulated ignition cable, an ignition cable shield, a terminal for thecable projecting from the shield adapted to conduct current to a sparkplug electrode, a sealed electrical connection between the terminal andcable, a flanged insulator sealed over the terminal end of the cable, amovable coupling to secure the cable shield to the spark plug shell ahollow, tubular spring carrier disposed over said flanged insulatorextending between the flange thereon and the cable shield and telescopicwithin the shield, and a compression spring pre-loaded to a fractionalpart of its free length confined by said carrier and compressiblebetween said carrier and the cable shield during tclescoping of thecarrier within the shield.

3. ln apparatus for connecting two radio shielded, insulated conductorsin the ignition system of an internal combustion engine or the like, thecombination with one of said conductors of an insulating sleevesurrounding an end portion of said one conductor and projecting from itsshielding enclosure, an annular flange on said sleeve for contact by theouter face thereof with an insulator of a second insulated conductor, atubular spring carrier disposed over said insulating sleeve intermediateof said annular flange and the shielding enclosure of said oneconductor, said carrier having a shoulder at one end to engage the innerface of the annular flange on said sleeve and having a shoulder on theopposite end thereof telescopic within said shielding enclosure, acompression spring member over said carrier deflected under stress to afraction of its free length and retained between the said end shouldersof the carrier, and a stepped recess in said shielding enclosureengaging one end of said spring, but permitting said carrier totelescope therein.

4. Apparatus adapted for use in combination with a spark plug includinga central electrode, a shielding shell and an insulator between saidelectrode and shell comprising a current conducting cable, a tubularshield for said cable, the latter terminating in a connector projectingfrom said shield and adapted to contact the spark plug electrode withinthe confines of said insulator, an insulating sleeve covering saidconducting cable within the spark plug shell and extending into thecable shield, said sleeve having a ange thereon to seal against theshell insulator, means to connect the cable shield and spark plug shell,a hollow, tubular spring carrier disposed over said sleeve between theange thereon and the cable `shield and being telescopic within theshield, and a compression spring pre-loaded on said carrier and furthercompressible between said carrier and the cable shield.

References Cited in the file of this patent UNITED STATES PATENTS

